The invention concerns artist's canvases, and particularly stretching frames and bracing systems for bracing the stretcher bars in medium and relatively large size canvas frames, to prevent pulling inward of the stretcher bars due to tension resulting from having stretched and tensioned the canvas.
The invention is concerned with generally the same subject matter as U.S. Pat. No. 6,520,240. The patent discloses a bracing system for large canvases, including those requiring more than two cross braces. As explained in the patent, braces have typically been used in a crossing configuration, with a pair of brace bars orthogonally arranged relative to the peripheral stretcher bars. Usually these bars were crossed over one another with routed out sections of each brace, such that the two crossing braces would notch together and lie in the same plane. Where the ends of the braces met the stretcher bars, typically each brace included a protruding tongue or tenon at its end, received in a routed out groove or mortise in the inside surface of the stretcher bar at that location. This would maintain the braces in place. In addition, and as shown in the patent, the ends of the braces could have a groove adjacent to the protruding tenon, allowing a tapered key or wedge to be inserted into the groove with enough force applied to spread the stretcher bar outward relative to the brace-end when needed, such as when the corners of the canvas frame have been keyed out to retighten the canvas.
FIGS. 1 and 2 show a conventional prior art brace system. As seen in FIG. 1, the upper and lower braces 10 and 12 are different, in that the joining notches 14 and 16 are at the bottom and the top, respectively, of these braces. These braces include a tongue or tenon 18 at each end, for extending into a corresponding groove or recess 17 in the side of a stretcher bar 19, to maintain each brace in proper position. A key or wedge could then be inserted into a notch 20 adjacent to the tongue at the end of each brace. This allowed the brace to be supported by the key and to push out or separate the brace-end from the stretcher bar as needed, by use of the key, while the tongue 18 remained in the groove of the stretcher bar. FIG. 2 shows the two cross braces assembled. The braces of U.S. Pat. No. 6,520,240 used this same basic principle.
There are problems with such a brace system in several important applications. Wood is traditionally used in the brace material, as well as for stretcher bars of the frame. It is a practical impossibility to construct braces for ¾ inch deep canvas frames, which are most of the frames sold in the marketplace, many being large frames that tend to require bracing. For ¾ inch frames the braces and wood components would have to be so small that the end features would be thin and susceptible to breakage. The braces must be thinner than the depth of the canvas frames, since they are spaced back from the back of the canvas.
Another problem is that illustrated in FIGS. 1 and 2 and discussed above. These drawings include examples of dimensions, but dimensions will vary. To provide a bracing system for use by consumers, two braces of different configurations would have to be provided such as shown in FIG. 1 (notch at top, notch at bottom), making this impractical for the retailer, who would have to carry two different braces for each length of stretcher bar, therefore doubling the required inventory.
It is a primary object of the invention to simplify bracing of canvas frames with the provision of only one style of brace for each length, and to provide bracing that can be used with ¾ inch depth stretcher frames, as well as frames of other depths.